1. Field of the Invention
The present invention relates to novel chemical compounds, and more specifically, it relates to a new class of pH sensitive indicator dyes. In a particular aspect, it relates to indicator dyes derived from certain 3,6-di-substituted carbazoles useful as optical filter agents in photographic processes for protecting an exposed photosenstive material from post-exposure fogging during development in the presence of extraneous incident light and to such photographic uses.
2. Description of the Prior Art
A number of photographic processes by which images may be developed and viewed within seconds or minutes after exposure have been proposed. Such processes generally employ a processing composition which is suitably distributed between two sheet-like elements, the desired image being carried by one of said sheet-like elements. The resulting images may be in black-and-white, e.g., in silver, or in one or more colors. Processing may be conducted in or outside of a camera. The most useful of such processes are the diffusion transfer processes which have been proposed for forming silver or dye images, and several of these processes have been commercialized. Such processes have in common the feature that the final image is a function of the formation of an image-wise distribution of an image-providing reagent and the diffusion transfer of said distribution to or from the stratum carrying the final image, whether positive or negative.
U.S. Pat. No. 3,415,644 discloses a composite photosensitive structure, particularly adapted for use in reflection type photographic diffusion transfer color processes. This structure comprises a plurality of essential layers including, in sequence, a dimensionally stable opaque layer; one or more silver halide emulsion layers having associated therewith dye image-providing material which is soluble and diffusible, in alkali, at a first pH, as a function of the point-to-point degree of its associated silver halide emulsion's exposure to incident actinic radiation; a polymeric layer adapted to receive solubilized dye image-providing material diffusing thereto; a polymeric layer containing sufficient acidifying capacity to effect reduction of a processing composition from the first pH to a second pH at which the dye image-providing material is substantially nondiffusible; and a dimensionally stable transparent layer. This structure may be exposed to incident actinic radiation and processed by interposing, intermediate the silver halide emulsion layer and the reception layer, an alkaline processing composition providing the first pH and containing a light-reflecting agent, for example, titanium dioxide to provide a white background. The light reflecting agent (referred to in said patent as an "opacifying agent") also performs an opacifying function, i.e., it is effective to mask the developed silver halide emulsions and also acts to protect the photoexposed emulsions from post-exposure fogging by light passing through the transparent layer if the photoexposed film unit is removed from the camera before image formation is complete.
In a preferred embodiment, the composite photosensitive structure includes a rupturable container, retaining the alkaline processing composition having the first pH and light-reflecting agent, fixedly positioned extending transverse a leading edge of the composite structure in order to effect, upon application of compressive pressure to the container, discharge of the processing composition intermediate the opposed surfaces of the reception layer and the next adjacent silver halide emulsion.
The liquid processing composition distributed intermediate the reception layer and the silver halide emulsion, permeates the silver halide emulsion layers of the composite photosensitive structure to initiate development of the latent images contained therein resultant from photoexposure. As a consequence of the development of the latent images, dye image-providing material associated with each of the respective silver halide emulsion layers is individually immobilized as a function of the point-to-point degree of the respective silver halide emulsion layer photoexposure, resulting in imagewise distributions of mobile dye image-providing materials adapted to transfer, by diffusion, to the reception layer to provide the desired transfer dye image. Subsequent to substantial dye image formation in the reception layer, a sufficient portion of the ions of the alkaline processing composition transfers, by diffusion, to the polymeric neutralizing layer to effect reduction in the alkalinity of the composite film unit to the second pH at which dye image-providing material is substantially nondiffusible, and further dye image-providing material transfer is thereby substantially obviated.
The transfer dye image is viewed, as a reflection image, through the dimensionally stable transparent layer against the background provided by the reflecting agent, distributed as a component of the processing composition, intermediate the reception layer and next adjacent silver halide emulsion layer. The thus-formed stratum effectively masks residual dye image-providing material retained in association with the developed silver halide emulsion layer subsequent to processing.
In the copending U.S. patent application Ser. No. 786,352 of Edwin H. Land, filed Dec. 23, 1968, now abandoned, and application Ser. No. 101,968 filed Dec. 28, 1970, now U.S. Pat. No. 3,647,437, in part a continuation of application Ser. No. 786,352, an organic light absorbing reagent (or optical filter agent), such as a dye, which is present as a light-absorbing species at the first pH and which may be converted to a substantially non-light-absorbing species at the second pH is used in conjunction with the light-reflecting agent to protect the selectively exposed silver halide emulsions from post-exposure fogging when development of the photo-exposed emulsions is conducted in the presence of extraneous incident actinic radiation impinging on the transparent layer of the film unit.
In copending U.S. Pat. application Ser. No. 108,260 filed Jan. 21, 1971, now U.S. Pat. No. 3,702,244, pH-sensitive dyes which contain at least one indole radical bonded by the 2- or 3-position to a ring-closing moiety are disclosed as useful as optical filter agents for absorbing incident radiation actinic to selectively exposed photosensitive materials within a predetermined wavelength range in the shorter wavelength region of the visible spectrum. Certain of the novel indicator dyes disclosed therein, namely, those derived from certain 3,6-di-substituted carbazoles are among the dyes comprising the subject matter of the present invention.